Gyrodactylus lilianae n. sp. (Polyonchoinea: Gyrodactylidae) from Rhamdia quelen (Quoy & Gaimard) (Siluriformes: Heptapteridae) from southern Brazil: a potential nuisance for aquaculture.

Species of Monogenoidea (Platyhelminthes) are in its majority ectoparasites of marine and freshwater fishes. Many species of the group can promote great economic losses to fish production systems worldwide. The present study describes a new species, Gyrodactylus lilianae n. sp., from the body surface, fins and barbels of a captive South American catfish, Rhamdia quelen (Quoy & Gaimard) (Siluriformes: Heptapteridae) from southern Brazil. The new species is morphologically similar to Neotropical species of Gyrodactylus von Nordmann, 1832 from Siluriformes from which it differs most conspicuously by the morphology of the hook with a pronounced convex heel, somewhat depressed, slightly pointed toe, and a small distal bulb. The identity of the new species is also strongly supported by phylogenetic analysis based on cytochrome c oxidase subunit 2 mitochondrial gene (cox2) sequences and the rDNA fragment ITS1-5.8-ITS2. Infections with the new species in captive R. quelen juveniles were considered the main causative agent of observed mortalities. Tissue damage caused by G. lilianae n. sp. apparently facilitated the occurrence of secondary infections by protists (Ichthyophthirius multifiliis) and bacteria (Aeromonas hydrophila).